Should I use h264parse/mpegvideoparse component prior to Elecard video decoders in my pipeline?

No, you shouldn't do that. A video parser can affect the performance of the pipeline.
For example, you can use such pipeline for receiving and decoding HLS stream:

gst-launch-1.0 ehlssrc location= http://10.10.30.5/channel2.m3u8 ! empgpdmx name=demux ! queue2 ! eavcdec ! videoconvert ! videoscale ! autovideosink demux. ! queue2 ! mpegaudioparse ! empegaudiodec ! pulsesink